You can change your default search engine in Firefox for Android. This article has the steps:

Manage my default search engines in Firefox for Android

Does that work for you?

I wish it worked. Mine is already set as default but doesn't stop google. When I tapped and held my search engine, I did not get magnifying glass on search bar.

cwpi said

Mine is already set as default but doesn't stop google.

So if you start entering some text to search in Firefox's address bar, and Firefox shows the icon of the current default search engine below the bar, it's not your default search engine, it's still the "G"?

When I tapped and held my search engine, I did not get magnifying glass on search bar.

Sorry, where did you tap and hold??

Let's say you want to add Startpage.com and make it your default.

When you load the site's home page, long-press the search box in the page and Firefox should display a bar that has the options:

PASTE     ADD SEARCH ENGINE

When you tap Add Search Engine, Firefox should display an overlay asking you to confirm and allowing you to edit the name.

Then when you go to

menu > Settings > Search

the newly added search engine should be listed and you can tap it and choose Set as default.

Does that work any better?